The invention relates to a transmission for transmitting torque from a drive or input element to a driven or output element where the input element and the output element rotate about a common axis of rotation. The input element and the output element are rotatably mounted in a housing, and the input element has at least one radially outwardly directed peripheral surface engaging at least one drive section of a number of transmission elements. That the output element forms an array of a predetermined number of radially inwardly open recesses angularly equispaced about the axis and forming a contact surface for at least one driven section of the transmission elements. The transmission elements are radially displaceable in guides of at least one retaining element fixed in or on the housing. The number of transmission elements and the number of recesses are not the same.
Transmissions with which torque can be transmitted have been described in a wide variety of embodiments in the prior art. In most cases, the goal is for the transmission to have a transmission ratio that allows the input and the output shaft to rotate at different speeds.
In classical spur gears, there is linear contact on the tooth flanks of the gears involved during the transmission of torque. A high transmission ratio can usually be implemented only by using multiple spur gear stages. With a worm gear that advantageously allows high transmission ratios, there is point contact between the worm gear and the worm in the transmission of torque, which thus limits the torque that can be transmitted. In addition transmissions having a coaxial drive shaft and output shaft, referred to as so-called cyclo or harmonic drives are also known. With them, high transmission ratios can be achieved, but only relatively low torques can be transmitted.
In many mechanical engineering applications the goal is to transmit high torque at a high gear transmission ratio. This should also be possible even under a sudden load and should not result in high wear in the transmission. The above-described known designs of transmissions always fulfill these requirements only partially and in particular the transmissible torque is usually very limited so that the above-described solutions are not suitable for heavy machinery.
To remedy this situation, transmissions of the above-described type which are suitable for transmission of high torques as well as having a high transmission ratio have become known. One such transmission is described in U.S. Pat. No. 6,416,438, for example. To be able to transmit high torque at a high transmission ratio, rod-like radially displaceable transmission elements are displaced radially in a cyclic manner during operation by a cam that bears radially outward on them and is formed as an eccentric circular surface. The transmission elements each have a roller on their radial outer end engaging in the recesses of the output element. Since there are more recesses than transmission elements, the output element is rotated by a defined angle per revolution of the input element. Based on this effect a desired high transmission ratio is achieved, and high torques can be transmitted. US 2009/0205451 shows a similar system.
One disadvantage of these transmissions is that the construction effort and the technical complexity of the device are quite high and the transmissions are as a result expensive. This is due to the plurality of rod-like and radially displaceable transmission elements for each of which a precise but nevertheless smooth support bearing must be provided.